The colossal squid shares features common to all squids: a mantle for locomotion, one pair of gills, and certain external characteristics like eight arms and two tentacles, a head, and two fins. 5 Conservation status and human interactions.4.1.3.1 Defrosting and dissection, April–May 2008.Captured in 2007, the largest colossal squid weighed 495 kilograms (1,091 lb), and is now on display with a second specimen at the Museum of New Zealand Te Papa Tongarewa. In 1981, an adult specimen was discovered, and in 2003 a second specimen was collected. The first specimens were discovered and described in 1925. It is presumed to be an ambush predator, and is a major prey of the sperm whale. Although little is known about the behaviour, it is known to use bioluminescence to attract prey.

It is known to inhabit the circumantarctic Southern Ocean. The species has similar anatomy to other members of its family although it is the only member of Cranchiidae to display hooks on its arms and tentacles. Maximum total length has been estimated at 10–14 metres (33–46 ft). The species is confirmed to reach a mass of at least 495 kilograms (1,091 lb), though the largest specimens-known only from beaks found in sperm whale stomachs-may perhaps weigh as much as 600–700 kilograms (1,300–1,500 lb), making it the largest known invertebrate. It is the only recognized member of the genus Mesonychoteuthis and is known from only a small number of specimens. It is sometimes called the Antarctic squid or giant cranch squid and is believed to be the largest squid species in terms of mass. The colossal squid ( Mesonychoteuthis hamiltoni) is part of the family Cranchiidae.

Group of squids